This invention relates to injection molding and more particularly to a filter assembly through which the hot molten plastic material passes between the molding machine to the mold.
The hot molten plastic material or melt may contain contaminants such as wood, paper, cardboard, iron, string, steel or brass which may plug the orifices or gates and consequently it is necessary to filter the melt as it leaves the molding machine. In the past, various devices have been used for this purpose. Thin mesh screens located in front of orificed retaining plates have the disadvantage that the screen breaks down and itself becomes a contaminant. Other devices such as radial filters have a considerable number of parts and are accordingly costly to manufacture and replace. Some of these previous filters have been provided with purging mechanism, but these similarly have the disadvantage of being relatively costly and also are subject to malfunction. Many of the prior art filters also have the disadvantage that there is a considerable pressure drop across them, thereby necessitating that a molding machine with a higher pressure output be utilized to achieve the same pressure at the mold gate.